On a local internet forum there is a lot of interest for an item I've designed especially for them. At the moment I'm at 47 items in the strong and flexible material in white, red and blue (nobody wants purple or pink).

So I was wondering if there is a policy or something for discount on bulk orders?

No. There's no discount for 10, 100 or 1000 of an item. The prices here are purely based upon the volume of material you consume.

You can save some on the setup fee if you put multiple copies of an item into a single file, but they (should) be joined together such that the operators can deal with them as a single unit. This process is normally referred to as adding "sprues" - thin wires between the items, or in some cases if you wrap a container around the items (think wire basket) that would contain them.

Patience, Persistance, Politeness - the 3Ps will help us get us to Perfect Printed Products

There's also a volume discount on models over 20cc with a density if 10% or more for the strong & flexible.
From http://www.shapeways.com/materials/strong-flexible;
"We also offer a volume and density discount on Strong & Flexible materials. For models that are greater than 10% dense (material volume divided by bounding box volume), after the first 20cm3, the remaining volume is calculated with a 50% discount."

What you could do is say you wanted 20 Red, 20 Blue and 7 White, make 3 files to upload and buy.
Place 20 of the Models as close as you can together using as little space, then create a bounding cage like structure around them to make it easier for handling when they've been printed.
This way you'll save $28.50 on the startup costs and depending on how much material you use you may make a saving with the volume discount.
(I think it would be roughly $66 saved on startup costs used this way)
Hope this helps,
Tom.

I generelly design 10x pieces containing 10 items of the same type.
For this issue I also have a blender script adding the sprues

So I save 13.5 of costs, which is in my case a significant price reduction.

Still waiting of a shapeway feature doing that. it has been asked for a couple of times.
- enabling sprues
- a 2nd stl containing the item on a sprue
- defining the expand direction, 2 items where placed along this axis, the ends of the sprue have to overlap

could be a simple method which is sufficient for my items. maybe somebody needing that can check it ....